<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <button>点击我发送post请求的ajax</button>
  <script>
    let btn = document.querySelector('button');
    btn.onclick = function () {
      let xhr = new XMLHttpRequest();
      xhr.open("post", "/postdata");
      xhr.setRequestHeader("content-type", "application/json");
      xhr.send("type");
      xhr.onload = function () {
        if (xhr.status >= 200 && xhr.status < 300) {
          console.log(xhr.responseText);
        }
      }
    }

  </script>
</body>

</html>